1. Field of the Invention
The present invention relates to a surveying instrument having an optical distance meter and an autofocus system which moves the focusing lens of the sighting telescope in accordance with the location of the sighting object, and also relates to a surveying instrument having a detachable autofocus system.
2. Description of the Related Art
When a surveyor measures the distance between two points with a surveying instrument such as a total station, a reflecting prism such as a corner cube is often used together with the surveying instrument. After the operator of the surveying instrument directs the sighting telescope to the reflecting prism and sights the reflecting prism through the sighting telescope, the distance measuring system (EDM) incorporated in the surveying instrument starts operating at the push of a distance measurement start button provided on the surveying instrument. Upon the commencement of the operation of the distance measuring system, a measuring light such as laser beam is projected from the surveying instrument toward the reflecting prism, and is reflected thereby to be eventually received by a light-receiving sensor in the surveying instrument. The distance measuring system calculates the distance to the reflecting prism via the phase difference between the projecting light and the received light.
A surveying instrument such as a total station is generally provided with a sighting telescope. Conventionally, the focusing lens of the sighting telescope is manually moved to focus the sighting telescope on a sighting object such as a reflecting prism. However, in recent years, surveying instruments equipped with an autofocus system which automatically moves the focusing lens to an in-focus position with respect to the sighting object have been proposed and developed.
With this type of surveying instrument equipped with an autofocus system, the sighting object is brought into focus automatically at the push of an AF start button after the operator aims the sighting telescope at the sighting object.
In a surveying instrument equipped with a phase detection type autofocus system, it is sometimes the case that the sighting object is unable to be brought into focus if the sighting object is like a white wall having no contrast, or a reflecting prism such as a corner cube.
If the sighting object is unable to be brought into auto-focus with the use of reflecting prism, the operator can try to perform the distance measuring operation with the autofocus system without the use of reflecting prism. However, in the case of the distance measuring operation being performed with the autofocus system without the use of reflecting prism, if infrared rays are used as measuring light that is to be projected toward the sighting telescope, the point of reflection of the infrared rays at the point of measurement cannot be visually confirmed, so that the point of measurement cannot be determined precisely.
When a distance measurement such as tracking distance measurement operation (consecutive distance measurement operation) is performed with a surveying instrument such as a total station which is equipped with an autofocus system, the distance measurement operation is performed with the surveying instrument in a manner such as shown in the flow chart in FIG. 9.
Firstly, the specified distance and other design data that are necessary for the tracking distance measurement operation are input to a controller of the surveying instrument via devices such as a design value input device and a measured distance (specified value) input device (step, SA1).
Subsequently, a distance measurement start button is depressed to start the distance measurement operation. For instance, the tracking distance measurement mode is set at the push of the distance measurement start button (step SA2). After the tracking distance measurement mode is set, the measured distance value is determined immediately after the measuring light reflected by the target returns to the surveying instrument, while the measured distance and the deviation between the input design value and the measured distance to the target are indicated on an indicating device.
Subsequently, when the sighting telescope is not aimed at the target, a sighting operation is performed (step SA3). In the sighting operation, the operator manually aims the sighting telescope at the target so that the optical axis of the sighting telescope is generally in line with the target while viewing the target through a collimator (not shown) which is attached to the sighting telescope. If the sighting telescope is in an in-focus state on the target, the operator manually operates the sighting telescope to sight the center of the target via the sighting telescope.
Subsequently, it is determined whether the AF start button is depressed (step SA4). The AF start button is depressed if the operator desires to bring the target into focus after the sighting operation is performed.
The autofocus system starts operating immediately after the AF start button is depressed. After the AF button is depressed, it is determined whether the target is in focus (step SA5). If it is determined that the target is in focus, control proceeds to step SA7.
If it is determined at step SA5 that the target is not in focus, control proceeds to step SA6 at which a focusing lens is automatically moved to a predetermined default position thereof to bring an object at a predetermined distance, which is stored as a default distance value in a conventional default-distance setting device, into focus.
After the target has been brought into focus, the measured distance value is determined while the sighting operation is being performed, and subsequently it is determined whether the measured distance value has been determined (step SA7). Namely, the measured distance value is determined immediately after the measuring light reflected by the target returns to the surveying instrument. Control proceeds to step SA8 if the measured distance value has been determined at step SA7. Control proceeds to step SA9 if the measured distance value has not yet been determined at step SA7.
If it is determined at step SA7 that the measured distance value has been determined the measured distance and the deviation between the input design value (specified distance) and the measured distance to the target are calculated to be indicated on the indicating device (step SA8). Consequently, the operator can identify the deviation between the current location of the target and the staking point by looking at the indicating device. This makes it possible for the operator of the surveying instrument to instruct the worker who holds the target to move the target in accordance with the deviation.
Thereafter, at the moment the deviation indicated on the indicating device becomes zero, the stakeout operation, in which the target is staked out at a staking point, is completed. Accordingly, after the operation at step SA8, it is determined whether a distance measurement stop button is depressed (step SA9) The operator pushes the distance measurement stop button if it is determined that the stakeout operation, in which the target is staked out at a staking point, is completed. If the distance measurement stop button is depressed during the sighting operation, control proceeds to step SA10 and the tracking distance measurement operation is terminated. Otherwise, control returns to step SA4 from step SB9 to repeat the operations from step SB4 to step SB9.
Accordingly, when a distance measurement such as a tracking distance measurement (consecutive distance measurement), consecutive distance stakeout measurement, or lot staking measurement is performed, the AF start button must be pushed frequently while the distance measurement is performed repetitively. However, it is troublesome for the operator to push the AF start button frequently. Furthermore, having to push the AF start button frequently hinders the target tracking operation.
Under such circumstances, it is difficult for the operator to concentrate on the target tracking operation and to finish the target tracking operation promptly with a conventional surveying instrument such as a conventional total station. For instance, if the line of sight of the sighting telescope deviates from the target to thereby make it impossible to bring the target into focus automatically during the stakeout operation, the focusing lens of the sighting telescope is generally moved to be focused on an object at a predetermined distance. However, it is often the case that such a predetermined distance is not at all related to any points for the stakeout operation, which makes it difficult to perform the stakeout operation promptly.
Various types of surveying instruments such as total stations having a sighting telescope have been developed. In a typical surveying instrument, the focusing lens of the sighting telescope is manually moved to adjust the focus of the sighting telescope. In recent years advanced surveying instruments equipped with an autofocus system which drives the focusing lens of the sighting telescope to adjust the focus thereof automatically have been developed.
In order to incorporate such an autofocus system into surveying instrument, it is necessary to provide the surveying instrument with a sensor (e.g., a multi segment CCD line sensor) for gaining information on the focal point of the sighting telescope, a lens driver having gears and a motor which drives the focusing lens of the surveying instrument in accordance with the information on the focal point of the sighting telescope, a controller for controlling the operation of the lens driver, and a hand operated member such as an AF start button to enable activation of the autofocus system.
However, the task of incorporating such an autofocus system into surveying instrument is time-consuming because elements of the autofocus system need to be connected to associated internal elements of the surveying instrument mechanically, electrically and optically. Moreover, the built-in autofocus system generally complicates the internal structure of the surveying instrument, which increases the possibility of the surveying instrument breaking down.
If the built in autofocus system breaks down, it is generally the case that the autofocus system needs to be repaired with one or more exterior covers of the surveying instrument being uncovered. Furthermore, one or more exterior covers of the surveying instrument need to be uncovered even when the autofocus system is inspected. This is obviously a troublesome task.
If such a surveying instrument equipped with an autofocus system and a conventional type surveying instrument equipped with no autofocus system are manufactured at the same time, these two types of surveying instruments normally need to be manufactured in different production lines because the autofocus system cannot be simply separated from the conventional surveying instrument to produce the surveying instrument equipped with an autofocus system. This increases the cost of production.
In conventional surveying instruments equipped with an autofocus system, a battery (a main electric power source) accommodated in the body of the surveying instrument supplies power to a lens drive motor of the autofocus system. Therefore, if battery of the surveying instrument runs out, the lens drive motor is not supplied with power, and consequently the autofocus system becomes dysfunctional.